The present invention generally relates to flight simulators and, more particularly, to visual systems for high performance military flight simulators.
Users of high performance military flight simulators are demanding higher resolution visual systems in order for the viewer, or pilot, to be able to distinguish air and ground targets and other features. For example, air combat applications may call for the high-resolution display of many simultaneous eye-limiting targets. Also, for example, ground attack applications may call for a large region of terrain to be displayed at a high resolution as well as one or more air targets. In general, higher resolution displays are more expensive, requiring more complicated hardware than that required to provide lower resolution displays. For example, a high-resolution image generator that puts high resolution everywhere incurs a high cost that comes from computing a high-resolution image in areas of the viewer's visual field of view where the human visual system can only see low resolution. The additional expense for the higher resolution systems required to achieve the training objectives requiring higher resolution, combined with budget limitations, may lead to fewer systems being purchased than the number required to train a sufficient number of pilots to meet the objectives.
A common strategy to address the economic problem of providing high resolution display is to provide high resolution display only in an area of interest (AOI) determined by the direction of the pilot's head position and, ideally, the direction of the eye's gaze. By providing high-resolution display over a small area and lower resolution display everywhere else, the requirement for more complicated hardware can be reduced and cost savings achieved. Implementation of this strategy, however, is not without difficulties. For example, one implementation of this strategy may use a background projector for displaying the low-resolution portion of the image and an area of interest, or AOI, projector for displaying the high-resolution portion of the image. The following disadvantages, for example, may be exhibited in such an implementation. The AOI projector and its associated background projector typically require careful dynamic intensity correction to assure that distracting color and intensity mismatches don't occur. Also, the AOI projector, being an analog device, is subject to drift between colors of the AOI and background images. Finally, the AOI projector, although requiring less complicated hardware than would be required for providing high resolution everywhere, still requires a significant amount of hardware.
One example of a prior art implementation of the AOI projector is known as the mechanically slewed AOI projector. The mechanically slewed AOI projector comprises a high-resolution inset projector and a low-resolution background projector that are optically combined through a servo driven projection head. Disadvantages include cost and reliability of the moving projection head and difficulty in matching colors and intensities between the AOI and background projectors. The mechanically slewed AOI projector is limited to use with front projection dome or mini-dome type systems, which also limits the potential for high image contrast.
Another example prior art implementation of the AOI projector is known as the electronically slewed AOI projector. The electronically slewed AOI projector system uses one or more electronically slewed AOI projectors to provide a green or a red/green inset over a low-resolution full color background image. The system may be designed for a rear projection display system made up of several smaller field of view screens abutted to form a full field of view display. A blue inset is generally not required because of the relatively small contribution of blue color required to present a high detail image. Disadvantages include the cost of additional projectors for each of the fields of view and a relatively complex alignment process for intensity and position.
Other prior art approaches include that of matrixing limited capability personal computer (PC) based image generators into one larger field of view by using a common field buffer memory or by optically combining the image generator fields of view directly on a projection screen. These approaches, like the approach of the high resolution image generator that puts high resolution everywhere, incur a cost disadvantage that comes from computing a high resolution image in areas where the human visual system can only see low resolution.
Another prior art approach includes placing high-resolution targets as an inset into background image in digital memory. For example, one implementation is a memory management device in which a set of individual high-resolution targets are written over a lower resolution background. Targets are specifically selected for high resolution, and as a result, the benefits of the approach are limited due to the inability to assure that the eye's high-resolution fovial region is always presented with a high-resolution simulated image. One implementation has a second mode in which an entire field of view, in an array of fields of view, is selected for high-resolution presentation.
As can be seen, there is a need for low cost high-resolution image generation for high performance flight simulators. There is also a need for low cost high-resolution image generation that is totally digital rather than incorporating analog or electromechanical-optical techniques. Moreover, there is a need for low cost high-resolution digital image generation, which is efficient by not generating high-resolution images in areas where the human visual system can only see low resolution.